1. Field of the Invention
The invention relates to a robot safety monitor device and a robot safety monitor method that monitor safety at the time of a tool change of a robot.
2. Description of the Related Art
Robot safety monitor devices for monitoring whether or not a movement path of a taught reference point of a robot is within a predetermined safe range that does not interfere with other objects, for example, the devices described in Japanese Patent No. 2662864 and Published Japanese Translation of PCT application No. 2001-525263 (JP-A-2001-525263), etc., have been widely known. In these devices, the robot is emergently stopped if the taught reference point where the robot receives a movement command is not within an action-permitted range.
However, the foregoing technologies of Japanese Patent No. 2662864 and Published Japanese Translation of PCT application No. 2001-525263(JP-A-2001-525263) are designed to monitor the movement path of a taught reference point, such as a tool's distal end, or the like, and no technology that improves the safety in conjunction with the change of tools has been developed. A robot control device controls the position and the speed of a taught reference point of a robot, and the posture of a tool, and outputs the angles of various axes of the robot to a robot safety monitor device in real time. At this time, besides the angles of the axes, tool identification information for identifying the tool that is attached to the robot's flange is output to the robot safety monitor device in real time. As for the tool change, the robot control device alters the tool identification information and outputs it to the outside at the time point when a tool change program is started. After that, with regard to a new tool, the taught reference point of the tool's distal end or the like is newly set, and command values in the coordinates of the axes of the robot are computed such that the taught reference point moves on a predetermined movement path, and are output to a servo control device. The robot safety monitor device inputs the axis command values that are output from the robot control device in real time, and finds, from these values, the coordinates of the taught reference point, such as the tool's distal end or the like, in the actual space, and then monitors a movement path of the taught reference point in the actual space. When tools are changed, the position and the posture of a tool's distal end relative to the flange center change, so that a change also occurs regarding the equation of the conversion from the axis command values to the space coordinates of the taught reference point. Therefore, the robot safety monitor device inputs the tool identification information that is output from the robot control device in real time. When a tool is changed to another, the monitor device uses a new conversion equation that corresponds to the new tool to find from the axis command values the space coordinates of the taught reference point, such as the tool's distal end or the like, and then determines whether or not the movement paths of the space coordinates exist in the action permitted region.
Thus, when there occurs a change regarding the tool identification information that is output from the robot control device in real time, the robot safety monitor device determines that tools have been changed. However, the time when the attachment of a tool to a flange of the robot is completed is naturally different from the time point at which the robot control device outputs the identification information of the new tool. During a deviation period between the time of completion of the tool change in reality and the time when the robot control device outputs the new tool identification information, the taught reference point, such as the position of the tool's distal end or the like, that the robot safety monitor device manages is different from the actual one. This gives rise to a problem of the safety monitoring becoming insufficient. Thus, the position control or the monitoring of position is performed with respect to the taught reference point, such as a tool's distal end or the like. Therefore, if despite a tool change, the position of the distal end of the old tool or the like is still used as a basis for performing the position control or the safety monitoring, that position is different from the actual position of the distal end of the presently used tool, thus giving rise to a problem in safety.
Therefore, if the completion of attachment of a new tool to a flange of the robot is actually detected and then the detection signal is output, together with the tool identification information, to the robot safety monitor device, the tool identification information and the information regarding the time point of the tool change are provided in a redundant manner, so that safety will be improved. However, as for the robot safety monitor device, a time difference occurs between the tool identification information output from the robot control device, and the real tool attachment completion signal and the tool identification information that are newly input. Regarding this time difference, it is not clear how to perform safety monitoring.